Image sensor having lens type color filter and method for fabricating the same

ABSTRACT

The image sensor includes lens-type color filters having a uniform shape for a plurality of pixels. The image sensor includes a plurality of pixels formed in a substrate, a plurality of color filter housings formed over outer boundaries of the respective pixels, and a plurality of color filters filled in spaces defined by the respective color filter housings, wherein the clock filter housings surround edges of the respective color filters with a given curvature.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Korean Patent ApplicationNo. 10-2013-0094097, filed on Aug. 8, 2013, which is incorporated hereinby reference in its entirety.

BACKGROUND

1. Field

Exemplary embodiments of the present invention relate to a semiconductordesign technology, and more particularly, to an image sensor with alens-type color filter and a method for fabricating the same.

2. Description of the Related Art

An image sensor is a semiconductor apparatus which converts an opticalimage into an electric signal. The image sensor includes a plurality ofpixels. Typically, each pixel includes a stack structure comprising aphotoelectric device such as a photodiode (PD), a color filter (CF),which selectively transmits incident light having a specific wavelength,and a microlens (ML), which condenses the incident light on thephotoelectric device.

In order to reduce the loss of incident light caused by the microlens, alens-type color filter was introduced. The lens-type color filter may beemployed alone or in combination with a microlens to improve the abilityto condense the incident light. However, due to limitations in thefabricating process it is difficult to form all of the pixels having auniform shape of the lens-type color filter.

SUMMARY

Various exemplary embodiments are directed to an image sensor with alens-type color filter, which includes a plurality of pixels having auniform shape of the lens-type clock filter, and a method forfabricating an image sensor.

In an exemplary embodiment of the present invention, an image sensor mayinclude a plurality of pixels formed in a substrate, a plurality ofcolor filter housings formed over outer boundaries of the respectivepixels, and a plurality of color filters filled in spaces defined by therespective color filter housings, wherein the clock filter housingssurround edges of the respective color filters with a given curvature.

In another exemplary embodiment of the present invention, a method forforming an image sensor may include forming sacrificial patterns over asubstrate including a plurality of pixels, corresponding to therespective pixels, performing a reflow process on the sacrificialpatterns to have a round edge, forming a mold layer along a surface of astructure including the sacrificial patterns, patterning the mold layerusing mask patterns as an etching mask to form a plurality of colorfilter housings surrounding edges of the respective sacrificial patternswith a given curvature; removing the mask patterns and the sacrificialpatterns to form spaces defined by the color filter housings, andfilling the spaces with color filter materials to form a plurality ofcolor filters over the respective pixels.

According to the embodiments, in pixels, color filter housings areformed to have a uniform shape, and color filter materials aregap-filled in spaces defined by the color filter housings to formlens-type color filters. Thus, the lens-type color filters are formed tohave a uniform shape for substantially all of the pixels. Under such astructure, the pixels may have uniform properties (e.g. uniformcondensing capacity) and accordingly, the performance of the imagesensor may be improved.

In addition, according to the embodiment, the lens-type color filtersare formed without a reflow process of color filter material. Thus,disadvantages attributable to the reflow process, such as damage to thecolor filter, irregular shape of the color filter, complexity offabrication, etc. may be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an image sensor including alens-type color filter according to an exemplary embodiment of thepresent invention; and

FIGS. 2A-2G are cross-sectional views showing a method for fabricatingan mage sensor including a lens-type color filter according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION

Various embodiments will be described below in more detail withreference to the accompanying drawings. The present invention may,however, be embodied in different forms, and should not be construed asbeing limited to the embodiments set forth herein. Rather, theseembodiments are provided for illustrative purposes, and may be modifiedby those skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The drawings are not necessarily to scale, and in some instances,proportions may have been exaggerated in order to clearly illustratefeatures of the embodiments. When a first layer is referred to as being“on” a second layer or “on” a substrate, it not only refers to the casewhere the first layer is formed directly on the second layer or thesubstrate, but also to the case where a third layer is present betweenthe first layer and the second layer or the substrate.

Exemplary embodiments of an image sensor including a lens-type colorfilter and a method for fabricating the same will be described below.Typically, a lens-type color filter is formed by sequential processes ofdepositing a color filter material and patterning the material, and afollowing reflow process to form the patterned material in a lens shape(e.g., in a hemispherical shape). At this time, different color filtermaterials may be employed for different pixels since the pixels are tofilter incident light having different wavelengths. Since the colorfilter materials that form the pixels are different, it is difficult toform the lens-type color filters disposed in respective pixels to have auniform shape (or curvature). When the lens-type color filters of thepixels are formed to have a non-uniform shape, a disparity in properties(e.g., condensing capacity) occurs between pixels. In addition, thecolor filter material is susceptible to damage caused in the course ofthe reflow process. Thus, it is not easy to perform the reflow processproperly.

Exemplary embodiments of the present invention provide an image sensorin which the lens-type color filters for a plurality of pixels have auniform shape, and a method for forming such an image sensor. Accordingto the exemplary embodiments of the present invention, a plurality ofpixels configured to respond to different wavelengths of incident lightare provided over a substrate. Each pixel includes a color filter. Acolor filter housing having a given curvature is provided so as tosurround the outer boundary of the color filter. Specifically, the colorfilter housing serves as a mold defining (or limiting) the color filterto have a lens shape. The color filter may be gap-filled inside thecolor filter housing.

An image sensor includes a charge coupled device (CCD) and a switchingtype CMOS image sensor (CIS). In a CCD individual MOS capacitors arelocated close to each other, and charge carriers are stored in thecapacitors. CIS employs a CMOS technology, which is applied to a controlcircuit and a peripheral circuit of a signal processing circuit, to formas many MOS transistors as pixels and detect outputs using them. Theexemplary embodiments described below according to the present inventionmay apply to both the CCD and CMOS image sensor.

FIG. 1 is a cross-sectional view of an image sensor including alens-type color filter according to an exemplary embodiment of thepresent invention.

As shown in FIG. 1, the image sensor according to the exemplaryembodiment includes a substrate 110. The substrate 110, as a givenstructure, may include a plurality of pixels and photoelectric devicesPD formed in the respective pixels.

The image sensor further includes a buffer layer 120 formed on thesubstrate 110, a plurality of color filters 140 disposed over the bufferlayer 120 and the respective pixels to serve as micro lenses, and colorfilter housings 130 having a given curvature and surrounding outerboundaries of the color filters 140, respectively.

The pixels over the substrate 110 may include first, second, and thirdpixels, each responsive to incident light having a specific wavelengthdifferent from others. The color filters 140 may include first, second,and third color filters 141, 142 and 143 corresponding to the first, thesecond, and the third pixels, respectively.

For example, the first, the second, and the third pixels may be a redpixel, a green pixel, and a blue pixel, respectively. The first, thesecond, and the third color filters 141, 142 and 143 may be a redfilter, a green filter, and a blue filter, respectively. Alternatively,the first, the second, and the third pixels may be replaced with a cyanpixel, a yellow pixel, and a magenta pixel, respectively.

The substrate 110 may include a semiconductor substrate. Thesemiconductor substrate may have a single crystal structure and includea silicon-containing material. That is, the substrate 110 may include asilicon-containing material having a single crystal structure. Thephotoelectric device PD may include a plurality of stacked photoelectricconverting elements (not shown). Each of the photoelectric convertingelements may be a photo diode that includes an N-type doping region or aP-type doping region.

As the given structure, the substrate 110, which includes thephotoelectric device PD, may further include a signal generatingcircuit. The signal generating circuit generates an electric signalcorresponding to photoelectric charges generated from the photoelectricdevice PD, and it may include a plurality of transistors, multi-layeredmetal lines, and a plurality of plugs connecting them. The transistorsmay include a transfer transistor (TX), a selection transistor (SX), areset transistor (RX), and an access transistor (AX).

The buffer layer 120 formed over the substrate 110 may serve as aplanarization layer that eliminates a step difference, which is createdover the substrate 110 by the given structure thereof, and it mayfurther serve as an anti-reflection layer to the incident light. Thebuffer layer 120 may be an oxide layer, a nitride layer, an oxynitridelayer, or a stack layer thereof.

The color filters 140 selectively transmit incident light havingdifferent wavelengths for the respective pixels. The incident light issubject to color separation for the respective pixels by the colorfilters 140 and provided to the photoelectric device PD. The colorfilters may include organic materials such as Polyacetylene,Poly(p-phenylene), Polythiophene, Poly(3,4-ethylenedioxy thiophene)(PEDOT), Polypyrrole, Poly(p-phenylene sulfide), Poly(p-phenylenevinylene), Polythiophene Poly(thienylene vinylene), Polyaniline,materials equivalent thereto, or a combination thereof. The first, thesecond, and the third pixels are configured to respond to incident lighthaving different wavelengths. Accordingly, the first, the second, andthe third color filters 141, 142 and 143 may include differentmaterials.

The color filter housings 130 with a given curvature serve to define thecolor filters 140 in a lens form so that the color filters 140 may serveas microlenses. The color filter housings 130 may surround therespective filters along the outer boundaries of the respective filters.

The color filters 140 fill spaces created by the color filter housings130. Due to the color filter housings 130, the color filters 140 may beformed to have a uniform shape (that is, a uniform curvature) forsubstantially all pixels.

The color filter housings 130 may include an insulation layer. Theinsulation layer may include an oxide layer, a nitride layer, anoxynitride layer, or a stack layer thereof. The color filter housings130 refract incident light to a direction perpendicular to a surface ofthe photoelectric device PD to increase condensing capacity. The colorfilter housings 130 may further serve as anti-reflection layers. Toproperly perform this function, the color filter housings 130 may have arefractive index lower than that of the color filters 140 but higherthan that of air.

In addition, the color filter housings 130 prevent the color filters 140from being damaged. This function will be described below in greaterdetail.

The image sensor according to the exemplary embodiments may furtherinclude a protection layer 150 over the given structure, which includesthe color filters 140 and the color filter housings 130. The protectionlayer 150 may be formed to have a given thickness along a surface of thegiven structure, which includes the color filters 140 and the colorfilter housings 130. The protection layer 150 may include an insulationlayer such as an oxide layer, a nitride layer an oxynitride layer, or astack layer thereof.

The protection layer 150 may function as an anti-reflection layer inaddition to protecting the color filters 140 and the color filterhousings 130. The protection layer 150 may have a refractive index lowerthan those of the color filter housings 130 and the color filters 140and higher than that of air.

Although not shown, microlens may be further provided to becorresponding to the respective pixels. In that case, the protectionlayer 150 may be a planarization layer covering a surface of thesubstrate 110 including the color filters 140. The mircolens may furtherincrease condensing capacity when used along with the color filters 140.

As described above, by employing the color filter housings 130 with agiven curvature, the lens-type color filters may be formed in a uniformshape in substantially all pixels having the same size. Accordingly, animage sensor may be obtained where pixels have uniform properties (e.g.,condensing capacity).

Meanwhile, though not illustrated, in case where all pixels do not havethe same size, e.g., the first and third pixels have a first size whilethe second pixel has a second size larger than the first size, thelens-type color filters in the second pixel may be formed to have a sizelarger than the first and third pixels. However, even in this case, thecolor filter housings 130 may be formed to have a given curvature, andthe lens-type color filters may be formed in a uniform shape insubstantially all pixels but have a different size in each pixel.

Referring to FIGS. 2A to 2G, an embodiment of a method for forming theimage sensor including lens-type color filters shown in FIG. 1 will bedescribed below. The lens-type color filters may maintain a uniformshape for substantially all pixels by employing the color filterhousings.

FIGS. 2A to 2G are cross-sectional views showing an exemplary embodimentof a method for forming the image sensor employing lens-type colorfilters.

As shown in FIG. 2A, a given structure including photoelectric devicesPD is formed over a substrate 11 including a plurality of pixels, e.g.,first, second, and third pixels. The first, the second, and the thirdpixels may be a red pixel, a green pixel, and a blue pixel,respectively. The photoelectric devices may include photodiodes. Thegiven structure may further include a signal generating circuit thatincludes a plurality of transistors, a multi-layered metal line, and aplurality of plugs interconnecting them.

Then, a buffer layer 12 is formed over the substrate over which thegiven structure including the photoelectric devices PD is formed. Thebuffer layer 12 may serve as a planarization layer to eliminate a stepdifference caused over the substrate 11 by the given structure thereof.The buffer layer 12 may further serve as an anti-reflection layer. Thebuffer layer 12 may include an insulation material. For example, thebuffer layer 12 may include an oxide layer, a nitride layer, anoxynitride layer, or a stack layer thereof.

As shown in FIG. 26, sacrificial patterns 13 are formed over the bufferlayer 12. The sacrificial patterns 13 may be formed over the pixelswhile exposing the buffer layer 12 formed over outer boundaries of therespective pixels. The sacrificial patterns 13 may be formed of amaterial that is suitable for a reflow process, such as a photoresistmaterial. For example, a photoresist may be deposited over the bufferlayer 12, and an exposure and development process may be subsequentlyperformed in order to form the sacrificial patterns 13.

As shown in FIG. 2C, the reflow process is performed on the sacrificialpatterns 13 in order for the sacrificial patterns 13 to have a roundedge (i.e., convex curvature). That is, the reflow process results inlens-type sacrificial patterns 13 having a given curvature, that is,having a hemispherical form. Hereinafter, the lens-type sacrificialpatterns 13 with a given curvature resulting from the reflow processwill be denoted as the numeral reference ‘13A’.

The reflow process may be performed by a thermal treatment and iscontrolled so that neighboring sacrificial patterns 13A do not come intocontact with each other in the course of the reflow process. Since thesacrificial patterns 13 are formed of the same material, the lens-typesacrificial patterns 13A have the same form and curvature through thereflow process.

As shown in FIG. 2D, a mold layer 14 is formed to have a given thicknessalong the surface of the structure that includes the sacrificialpatterns 13A. The mold layer 14 may be formed to have a thickness suchthat it fills the space between neighboring sacrificial patterns 13A.

The mold layer 14 may include an insulation material. For example, themold layer 14 may include an oxide layer, a nitride layer, an oxynitridelayer, or a stack layer thereof. The mold layer 14 may include aninsulation layer whose refractive index is lower than that of the colorfilters, which will be formed in a subsequent process, and higher thanthat of air.

As shown in FIG. 2E, mask patterns 15 are formed over the mold layer 14.The mask patterns 15 may be formed in a manner such that they coveredges of the respective pixels and have openings in the centers of therespective pixels so that the mold layer 14 is exposed.

To simplify the fabrication process, the mask patterns 15 may be formedof the same material as the sacrificial patterns 13A. For example, themask patterns 15 may include a photoresist material. When a photoresistmaterial is employed, the photoresist material may be deposited over themold layer 14 and subject to an exposure and development process to formthe mask patterns 15.

The molder layer 14 is etched using the mask patterns 15 as an etchingbarrier to form color filter housings 14A. The color filter housings 14Amay have a concave curvature inside, corresponding to the convexcurvature of the sacrificial patterns 13A, and it may surround edges ofthe sacrificial patterns 13A. By using the sacrificial patterns 13A, thecolor filter housings 14A are formed in the same shape for substantiallyall pixels. Thus, the curvatures of the color filter housings 14A may besubstantially the same for all pixels.

As shown in FIG. 2F, the mask patterns 15 and the sacrificial patterns13A are removed. When the mask patterns 15 and the sacrificial patterns13A are formed of the same material, they may be remove at the sametime, thus simplifying the process. For example, when the mask patterns15 and the sacrificial patterns 13A are formed of a photoresist, theymay be removed at the same time by an ashing process or by oxide plasmatreatment.

Upon removing the mask patterns 15 and the sacrificial patterns 13A,spaces 16A, 16B and 16C are defined by the color filter housings 14Aformed along the outer boundaries of the respective pixels.Specifically, first, second, and third spaces 16A, 16B and 16C aredefined by the color filter housings 14A, corresponding to the first,the second, and the third pixels, respectively.

As shown in FIG. 2G, the spaces 16A, 16B and 16C defined by the colorfilter housings 14A are filled with color filter materials to form aplurality of color filters 17, 18 and 19.

Since the color filter housings 14A have the same curvature forsubstantially all pixels and the color filters 17, 18 and 19 are formedby filling the spaces 16A, 16B and 16C defined by the color filterhousings 14A, the color filters 17, 18 and 19 may have substantially thesame shape (that is, the same curvature) for all pixels. That is, byemploying the color filter housings 14A, the color filters 17, 18 and 19may be formed to have the same lens shape for substantially all pixels.

The color filter material may include an organic material such asPolyacetylene, Poly(p-phenylene), Polythiophene, Poly(3,4-ethylenedioxythiophene) (PEDOT), Polypyrrole, Poly(p-phenylene sulfide),Poly(p-phenylene vinylene), Polythiophene Poly(thienylene vinylene),Polyaniline, or an equivalent thereto.

Specifically, when the first, the second, and the third pixels are a redpixel, a green pixel, and a blue pixel, respectively, the first space16A is filled with a red filter material, the second space 16B is filledwith a green filter material, and the third space 16C is filled with ablue filter material, resulting in the color filters 17, 18 and 19.

The red filter material, the green filter material, and the blue filtermaterial are different materials from each other. Nevertheless, sincethe color filter materials are not subject to a reflow process, thecolor filter materials may be prevented from being damaged in the courseof the reflow process. In addition, the shapes of the color filters maybe prevented from being transformed in non-uniform manners due to thedifference in the color filter materials.

A protection layer 20 is formed over the color filters 17, 18 and 19 andthe color filter housings 14A. The protection layer 20 may be formed tohave a given thickness along a surface of the underlying structureincluding the color filters 17, 18 and 19 and the color filter housings14A.

The protection layer 20 may include an insulation material. For example,the protection layer 20 may include an oxide layer, a nitride layer, anoxynitride layer, or a stack layer thereof. The protection layer 20 mayprotect the color filters 17, 18 and 19 and the color filter housings14A, and further serve as an anti-reflection layer.

The protection layer 20 may include material whose refractive index issmaller than that of the color filter housings 14A and the color filters17, 18 and 19, and larger than that of air. Then, typical processes mayfollow to form an image sensor.

According to the embodiments described above, the color filter housings14A are formed to have a uniform curvature for substantially all pixels,and color filter materials are filled in the spaces 16A, 16B and 16Cdefined by the color filter housings 14A to form the lens-type colorfilters. As a result, the lens-type color filters are formed to have auniform shape for substantially all pixels.

In addition, since no reflow process is performed after the colorfilters are formed, disadvantages may be prevented from being caused bythe reflow process, such as damage to the color filters, non-uniformityof the color filters, reduction in production yield due to complicatedprocesses, etc.

Although various embodiments have been described for illustrativepurposes, it will be apparent to those skilled in the art that variouschanges and modifications may be made without departing from the spiritand scope of the invention as defined in the following claims.

What is claimed is:
 1. An image sensor comprising: a plurality of pixelsformed in a substrate; a plurality of color filter housings formed overouter boundaries of the respective pixels; and a plurality of colorfilters filled in spaces defined by the respective color filterhousings, wherein the color filter housings surround edges of therespective color filters with a given curvature.
 2. The image sensor ofclaim 1, further comprising: a protection layer formed over a resultantstructure including the color filters and the color filter housings. 3.The image sensor of claim 1, wherein the color filter housings have arefractive index larger than that of air and smaller than that of thecolor filters.
 4. The image sensor of claim 1, wherein the color filtersinclude first to third color filters, which are formed to have a convexcurvature corresponding to the given curvature.
 5. The image sensor ofclaim 2, wherein the protection layer has a refractive index larger thanthat of air and smaller than those of the color filters and the colorfilter housings.
 6. The image sensor of claim 4, wherein the first tothird color filters have the same curvature while having differentmaterials.